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<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        /*
            有点简单...
        */
        Array.prototype.myMap = function (callback) {
            const res = [];
            for(let i = 0;i < this.length;i ++) {
                res.push(callback(this[i], i, this));
            }
            return res;
        }
        const arr = [1, 2, 3];
        console.log(arr.myMap(item => item * 2)); // [2, 4, 6]
    </script>
</body>

</html>